Many useful applications, such as the detection of radioactive material and computer-assisted tomography (“CAT”), rely on the detection of photon radiation, known as X-ray and/or gamma-ray radiation. Both of these types of high-energy photon radiation cause ionization and for the purposes of this disclosure the two terms, X-ray and gamma-ray, are used interchangeably. In terms of the detection of such ionizing radiation, the spectral region of greatest interest for most of these applications generally falls between the energies of about 20 keV to 20 MeV. Other applications, including the detection of particle radiation from ion beam accelerators/colliders, cosmic ray generated minimum ionizing particles (“MIP”s), and neutrons from special nuclear materials (“SNM”) used in nuclear weapons (e.g., enriched uranium or plutonium-239), rely on the detection of ionizing particles that can be either atomic nuclei (e.g., alpha particles), or subatomic (e.g., neutrons, protons and muons) in nature, and which can vary over a very broad energy range from less than 1 MeV to well beyond 1 TeV.
In order to detect ionizing radiation in the above spectral range of interest, a number of known sensing devices are commonly used. One of the earliest known electronic devices is the ionization chamber. Detection of radiation in an ionization chamber, such as a Geiger-Mueller (“GM”) tube, is based upon electrical conductivity induced in an inert gas (usually containing argon, neon or helium as the main component) as a consequence of ion-pair formation. One currently widely used type of ionizing-particle radiation detector is the micropattern gas detector. These devices have been under continuous development for many years in high energy and nuclear physics. Detectors such as the Microstrip Gas Chamber (“MSGC”), Gas Electron Multiplier (“GEM”) and Micromegas have many desirable properties as proportional gas detectors, but are operationally limited to gains within the proportional region in the range of ˜103 to 106.